As I revealed exclusively on the Windows Weekly podcast back in January, Nokia's new flagship Windows Phone handset, the Lumia 900, will cost just $99 when it becomes available to the public. But Nokia missed its original release date of March 18 by three weeks: The device will now ship on April 8, the wireless carrier says.

"AT&T and Nokia’s relationship spans many years, and we’re thrilled to introduce their first 4G LTE Windows Phone only for our customers," said AT&T Senior Vice President Jeff Bradley. "The Lumia 900 is impeccably designed with clean lines and a camera that rivals standalone digital cameras on the market today. Combine that with the people-first Windows Phone experience and our4G LTE network—the nation's largest 4G network—and it’s clear that this is one of the best phones customers can find."

Nokia unveiled the Lumia 900 earlier this year, noting only that the device, which would be exclusive to AT&T for an unrevealed time period, would ship sometime in the first half of 2012. The Lumia 900 is the second Nokia-based Windows Phone handset to ship in the US, but it wasn't supposed to be that way. Sources tell me that Nokia originally slated its Lumia 800 to ship on AT&T in late 2011 but that that handset failed certain internal AT&T tests. It's unclear if the Lumia 900 delays are related.

Since then, the Nokia Lumia 710 has appeared on T-Mobile, but the Lumia 800 has remained an international curiosity only. The Lumia 900 takes everything that is right about the 800, however, and improves on it in sometimes dramatic ways. The Lumia 900 features true LTE/4G connectivity, for example, and both front- and rear-facing cameras. And that rear camera is a step up from the Lumia 800 model, offering 8 megapixels of resolution.

Although the Lumia 900 is clearly the most impressive and substantial Windows Phone offering to date, the most curious aspect of this device is its price: At just $99, it undercuts other "hero" phones by $200 to $300, so it should appeal to a much wider demographic than current high-end smartphones. That's the hope, at least: Another theory suggests that undercutting the price will ultimately harm the Windows Phone brand further by making the devices seem less desirable than the iPhone or high-end Android devices.

To help prevent that, Microsoft, Nokia, and AT&T are going to market the heck out of this thing. According to internal Microsoft marketing materials I exclusively reported on back in January, Microsoft and its hardware makers and wireless carrier partners are spending just under $200 million marketing various Windows Phone handsets during the first half of 2012 in the United States alone. And this one handset will account for about $90 million of that sum, with about two-thirds of that coming from Nokia.

The Lumia 900 will initially be available in matte black and cyan blue, and like the Lumia 800, a white version will be added to the lineup, in this case on April 22. Customers interested in preordering the handset can do so beginning March 30, AT&T said.